1. Field of the Invention
The present invention relates to semiconductor processing equipment, and more particularly, to a pump baffle and screen used to improve etch uniformity for processes utilized on that equipment.
2. Description of the Related Art
Two of the most common types of semiconductor processes are plasma etch and deposition. These processes are accomplished via the use of a sealed chamber wherein the silicon wafer or workpiece is transported into the chamber and is exposed to a variety of process gasses to perform various types of operations upon the workpiece. The process gasses are removed from the chamber via a pump. Many of the pumps in plasma etch and deposition chambers are asymmetrically located. That is, the location of the pump is such that gas exits the chamber on one side of the wafer or workpiece as opposed to symmetrically on all sides of the wafer. This asymmetric pumping can result in non-uniform etch rate or deposition rate because of the changing concentration of reacting species as the gas flows towards the pump.
Asymmetric pumping can also result in non-uniform plasma density and electrical potential across the wafer since the pump port represents a location on the boundary of the plasma where there is a non-solid wall. Plasma may stream into this discontinuity in the wall and cause a disruption in the potential or density profile that is characteristic of the rest of the chamber""s perimeter. FIG. 1 shows a typical etch rate map from an asymmetrically pumped chamber. It suggests that the presence of the pump port causes a non-uniform etch pattern that is aligned with the pump port. The arrows in the figure show the approximate direction of the gas flow as it exits the chamber through the pump port on the right.
One way to solve the asymmetric pumping effect is to design a chamber where the gas is pumped symmetrically around the entire perimeter of the wafer, often by placing the pump symmetrical to the workpiece. However, due to other design considerations this may not always be practical and this pump re-arrangement is not feasible in already existing chambers.
Accordingly, the present invention relates to a pump baffle and screen which can as a retrofit be placed in existing chambers or designed into new chambers to improve uniformity when asymmetric pump effect is a factor.
The present invention provides a pump baffle and screen that partially blocks the pump port. The baffle causes a flow restriction that reduces the asymmetric pumping effect. The baffle also provides enough wall surface area across the pump port to reduce the electrical irregularities caused by the abrupt discontinuation of the solid wall.